We suggest that a family of Ni-based compounds, which contain [Ni_2M_2O]~2à(M = chalcogen) layers with an antiperovskite structure constructed by mixed-anion Ni complexes, Ni M_4O_2, can be potential high tempera...We suggest that a family of Ni-based compounds, which contain [Ni_2M_2O]~2à(M = chalcogen) layers with an antiperovskite structure constructed by mixed-anion Ni complexes, Ni M_4O_2, can be potential high temperature superconductors(high-Tc) upon doping or applying pressure. The layer structures have been formed in many other transitional metal compounds such as La_2B_2Se_2O_3(B = Mn, Fe, Co). For the Ni-based compounds, we predict that the parental compounds host collinear antiferromagnetic states similar to those in iron-based high temperature superconductors. The electronic physics near Fermi energy is controlled by two egd-orbitals with completely independent in-plane kinematics. We predict that the superconductivity in this family is characterized by strong competition between extended s-wave and d-wave pairing symmetries.展开更多
We suggest that cobalt-oxychalcogenide layers constructed by vertex sharing CoA_2O_2(A = S, Se, Te) tetrahedra, such as BaCoAO, are strongly correlated multi-orbitals electron systems that can provide important clues ...We suggest that cobalt-oxychalcogenide layers constructed by vertex sharing CoA_2O_2(A = S, Se, Te) tetrahedra, such as BaCoAO, are strongly correlated multi-orbitals electron systems that can provide important clues on the cause of unconventional superconductivity. Differing from cuprates and iron-based superconductors, these systems lack of the D_(4h) symmetry classification. However, their parental compounds possess antiferromagnetic(AFM) Mott insulating states through pure superexchange interactions and the low energy physics near Fermi surfaces upon doping is mainly attributed to the three t_(2g) orbitals that dominate the AFM interactions. We derive a low energy effective model for these systems and predict that a d-wave-like superconducting state with reasonable high transition temperature can emerge by suppressing the AFM ordering even if the pairing symmetry can not be classified by the rotational symmetry any more.展开更多
We suggest a new family of Co[Ni-based materials that may host unconventional high temperature superconductivity （high-To）. These materials carry layered square lattices with each layer being formed by vertex-shared...We suggest a new family of Co[Ni-based materials that may host unconventional high temperature superconductivity （high-To）. These materials carry layered square lattices with each layer being formed by vertex-shared transition metal tetrahedra cation-anion complexes. The electronic physics in these materials is determined by the two dimensional layer and is fully attributed to the three near degenerated t2g d-orbitals close to a d7 filling configuration in the d-shell of CoJNi atoms. The electronic structure meets the necessary criteria for unconventional high Tc materials proposed recently by us to unify the two known high-Tc families, cuprates and iron-based superconductors. We predict that they host superconducting states with a d-wave pairing symmetry with Tc potentially higher than those of iron-based superconductors. These materials, if realized, can be a fertile new ground to study strongly correlated electronic Physics and provide decisive evidence for superconducting pairing mechanism.展开更多
Over the decade,Dirac semimetals(DSMs)have been extensively studied[1].However,the hallmarks of DSMs are still not clear[2,3].Recently,a generalized bulk-boundary correspondence,namely higher-order bulk-hinge correspo...Over the decade,Dirac semimetals(DSMs)have been extensively studied[1].However,the hallmarks of DSMs are still not clear[2,3].Recently,a generalized bulk-boundary correspondence,namely higher-order bulk-hinge correspondence,for DSMs[4–7]has been proposed,i.e.,one-dimensional(1D)higher-order Fermi arcs(HOFAs)are direct and topological consequences of 3D bulk Dirac points.The 3D bulk Dirac points lead to the nontrivial filling anomalyη[8,9]of the 2D insulating momentum-space plane away from them,which ensures the presence of gapless mid-gap states on 1D hinges.展开更多
At magic twisted angles,Dirac cones in twisted bilayer graphene(TBG)can evolve into flat bands,serving as a critical playground for the study of strongly correlated physics.When chiral symmetry is introduced,rigorous ...At magic twisted angles,Dirac cones in twisted bilayer graphene(TBG)can evolve into flat bands,serving as a critical playground for the study of strongly correlated physics.When chiral symmetry is introduced,rigorous mathematical proof confirms that the flat bands are locked at zero energy in the entire Moiré Brillouin zone(BZ).Yet,TBG is not the sole platform that exhibits this absolute band flatness.Central to this flatness phenomenon are topological nodes and their specific locations in the BZ.In this study,considering twisted bilayer systems that preserve chiral symmetry,we classify various ordered topological nodes in base layers and all possible node locations across different BZs.Specifically,we constrain the node locations to rotational centers,such as Γ and M points,to ensure the interlayer coupling retains equal strength in all directions.Using this classification as a foundation,we systematically identify the conditions under which Moiré flat bands emerge.Additionally,through the extension of holomorphic functions,we provide proof that flat bands are locked at zero energy,shedding light on the origin of the band flatness.Remarkably,beyond Dirac cones,numerous twisted bilayer nodal platforms can host flat bands with a degeneracy number of more than two,such as four-fold,six-fold,and eight-fold.This multiplicity of degeneracy in flat bands might unveil more complex and enriched correlation physics.展开更多
We predict Co-based chalcogenides with a diamond-like structure can host unconventional high temperature superconductivity(high-Tc). The essential electronic physics in these materials stems from the Co layers with ea...We predict Co-based chalcogenides with a diamond-like structure can host unconventional high temperature superconductivity(high-Tc). The essential electronic physics in these materials stems from the Co layers with each layer being formed by vertex-shared CoA_4(A=S, Se, Te) tetrahedra complexes, a material genome proposed recently by us to host potential unconventional high-Tcclose to a d7 filling configuration in 3 d transition metal compounds. We calculate the magnetic ground states of different transition metal compounds with this structure. It is found that(Mn, Fe, Co)-based compounds all have a G-type antiferromagnetic(AFM) insulating ground state while Ni-based compounds are paramagnetic metal.The AFM interaction is the largest in the Co-based compounds as the three t2 gorbitals all strongly participate in AFM superexchange interactions. The abrupt quenching of the magnetism from the Co to Ni-based compounds is very similar to those from Fe to Co-based pnictides in which a C-type AFM state appears in the Fe-based ones but vanishes in the Co-based ones. This behavior can be considered as an electronic signature of the high-Tcgene. Upon doping, as we predicted before, this family of Co-based compounds favor a strong d-wave pairing superconducting state.展开更多
We investigate superconductivity that may exist in the doped BaCoSO, a multi-orbital Mott insulator with a strong antiferromagnetie ground state. The superconductivity is studied in both t-J type and Hubbard type mult...We investigate superconductivity that may exist in the doped BaCoSO, a multi-orbital Mott insulator with a strong antiferromagnetie ground state. The superconductivity is studied in both t-J type and Hubbard type multi-orbital models by mean field approach and random phase approximation （RPA） analysis. Even if there is no C4 rotational symmetry, it is found that the system still carries a d-wave like pairing symmetry state with gapless nodes and sign changed superconducting order parameters on Fermi surfaces. The results are largely doping insensitive. In this superconducting state, the three t2g orbitals have very different superconducting form factors in momentum space. In particular, the intra-orbital pairing of the dx2-y2 orbital has an s-wave like pairing form factor. The two methods also predict very different pairing strength on different parts of Fermi surfaces. These results suggest that BaCoSO and related materials can be a new ground to test and establish fundamental principles for unconventional high temperature superconductivity.展开更多
基金supported by the Ministry of Science and Technology of China(2015CB921300 and 2017YFA0303100)the National Natural Science Foundation of China(1190020,11534014,and 11334012)+1 种基金the Strategic Priority Research Program of CAS(XDB07000000)the Key Research Program of the CAS(XDPB08-1)
文摘We suggest that a family of Ni-based compounds, which contain [Ni_2M_2O]~2à(M = chalcogen) layers with an antiperovskite structure constructed by mixed-anion Ni complexes, Ni M_4O_2, can be potential high temperature superconductors(high-Tc) upon doping or applying pressure. The layer structures have been formed in many other transitional metal compounds such as La_2B_2Se_2O_3(B = Mn, Fe, Co). For the Ni-based compounds, we predict that the parental compounds host collinear antiferromagnetic states similar to those in iron-based high temperature superconductors. The electronic physics near Fermi energy is controlled by two egd-orbitals with completely independent in-plane kinematics. We predict that the superconductivity in this family is characterized by strong competition between extended s-wave and d-wave pairing symmetries.
基金supported by the National Basic Research Program of China (2015CB921300)the National Natural Science Foundation of China (11334012)the Strategic Priority Research Program of Chinese Academy of Sciences (XDB07000000)
文摘We suggest that cobalt-oxychalcogenide layers constructed by vertex sharing CoA_2O_2(A = S, Se, Te) tetrahedra, such as BaCoAO, are strongly correlated multi-orbitals electron systems that can provide important clues on the cause of unconventional superconductivity. Differing from cuprates and iron-based superconductors, these systems lack of the D_(4h) symmetry classification. However, their parental compounds possess antiferromagnetic(AFM) Mott insulating states through pure superexchange interactions and the low energy physics near Fermi surfaces upon doping is mainly attributed to the three t_(2g) orbitals that dominate the AFM interactions. We derive a low energy effective model for these systems and predict that a d-wave-like superconducting state with reasonable high transition temperature can emerge by suppressing the AFM ordering even if the pairing symmetry can not be classified by the rotational symmetry any more.
基金supported by the National Basic Research Program of China (973 Program) (2015CB921300)the National Natural Science Foundation of China (11334012)the Strategic Priority Research Program of Chinese Academy of Sciences (XDB07000000)
文摘We suggest a new family of Co[Ni-based materials that may host unconventional high temperature superconductivity （high-To）. These materials carry layered square lattices with each layer being formed by vertex-shared transition metal tetrahedra cation-anion complexes. The electronic physics in these materials is determined by the two dimensional layer and is fully attributed to the three near degenerated t2g d-orbitals close to a d7 filling configuration in the d-shell of CoJNi atoms. The electronic structure meets the necessary criteria for unconventional high Tc materials proposed recently by us to unify the two known high-Tc families, cuprates and iron-based superconductors. We predict that they host superconducting states with a d-wave pairing symmetry with Tc potentially higher than those of iron-based superconductors. These materials, if realized, can be a fertile new ground to study strongly correlated electronic Physics and provide decisive evidence for superconducting pairing mechanism.
基金supported by the National Natural Science Foundation of China(11974076,11925408,11921004,and 12188101)the Key Project of Natural Science Foundation of Fujian Province(2021J02012)+4 种基金the Ministry of Science and Technology of China(2018YFA0305700)the Chinese Academy of Sciences(XDB33000000 and CAS-WX2021SF-0102)the K.C.Wong Education Foundation(GJTD-2018–01)the Key Research Project of Zhejiang Lab(2021PB0AC01)supported by the Swiss National Science Foundation(200021–196966)。
文摘Over the decade,Dirac semimetals(DSMs)have been extensively studied[1].However,the hallmarks of DSMs are still not clear[2,3].Recently,a generalized bulk-boundary correspondence,namely higher-order bulk-hinge correspondence,for DSMs[4–7]has been proposed,i.e.,one-dimensional(1D)higher-order Fermi arcs(HOFAs)are direct and topological consequences of 3D bulk Dirac points.The 3D bulk Dirac points lead to the nontrivial filling anomalyη[8,9]of the 2D insulating momentum-space plane away from them,which ensures the presence of gapless mid-gap states on 1D hinges.
基金supported by Japan Science and Technology Agency(JST)as part of Adopting Sustainable Partnerships for Innovative Research Ecosystem(Grant No.JPMJAP2318)the JST Presto(Grant No.JPMJPR2357)+5 种基金supported by the National Key R&D Program of China(Grant No.2022YFA1403901)the National Natural Science Foundation of China(Grant No.11888101)the National Natural Science Foundation of China(Grant No.12047503)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB28000000 and XDB33000000)the New Cornerstone Investigator Programsupported by the National Key R&D Program of China(Grant No.2023YFA1407300)。
文摘At magic twisted angles,Dirac cones in twisted bilayer graphene(TBG)can evolve into flat bands,serving as a critical playground for the study of strongly correlated physics.When chiral symmetry is introduced,rigorous mathematical proof confirms that the flat bands are locked at zero energy in the entire Moiré Brillouin zone(BZ).Yet,TBG is not the sole platform that exhibits this absolute band flatness.Central to this flatness phenomenon are topological nodes and their specific locations in the BZ.In this study,considering twisted bilayer systems that preserve chiral symmetry,we classify various ordered topological nodes in base layers and all possible node locations across different BZs.Specifically,we constrain the node locations to rotational centers,such as Γ and M points,to ensure the interlayer coupling retains equal strength in all directions.Using this classification as a foundation,we systematically identify the conditions under which Moiré flat bands emerge.Additionally,through the extension of holomorphic functions,we provide proof that flat bands are locked at zero energy,shedding light on the origin of the band flatness.Remarkably,beyond Dirac cones,numerous twisted bilayer nodal platforms can host flat bands with a degeneracy number of more than two,such as four-fold,six-fold,and eight-fold.This multiplicity of degeneracy in flat bands might unveil more complex and enriched correlation physics.
基金supported by the Ministry of Science and Technology of China(2015CB921300 and 2017YFA0303100)the National Natural Science Foundation of China(11334012)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB07000000)
文摘We predict Co-based chalcogenides with a diamond-like structure can host unconventional high temperature superconductivity(high-Tc). The essential electronic physics in these materials stems from the Co layers with each layer being formed by vertex-shared CoA_4(A=S, Se, Te) tetrahedra complexes, a material genome proposed recently by us to host potential unconventional high-Tcclose to a d7 filling configuration in 3 d transition metal compounds. We calculate the magnetic ground states of different transition metal compounds with this structure. It is found that(Mn, Fe, Co)-based compounds all have a G-type antiferromagnetic(AFM) insulating ground state while Ni-based compounds are paramagnetic metal.The AFM interaction is the largest in the Co-based compounds as the three t2 gorbitals all strongly participate in AFM superexchange interactions. The abrupt quenching of the magnetism from the Co to Ni-based compounds is very similar to those from Fe to Co-based pnictides in which a C-type AFM state appears in the Fe-based ones but vanishes in the Co-based ones. This behavior can be considered as an electronic signature of the high-Tcgene. Upon doping, as we predicted before, this family of Co-based compounds favor a strong d-wave pairing superconducting state.
基金This work was supported by the National Basic Research program of the Ministry of Science and Technology of China （973 Program, Grant No. 2015CB921300）, the National Natural Science Foundation of China （Grant Nos. NSFC-1190020, 11534014, 11334012）, and the Strategic Priority Research Program of CAS （Grant No. XDB07000000）.
文摘We investigate superconductivity that may exist in the doped BaCoSO, a multi-orbital Mott insulator with a strong antiferromagnetie ground state. The superconductivity is studied in both t-J type and Hubbard type multi-orbital models by mean field approach and random phase approximation （RPA） analysis. Even if there is no C4 rotational symmetry, it is found that the system still carries a d-wave like pairing symmetry state with gapless nodes and sign changed superconducting order parameters on Fermi surfaces. The results are largely doping insensitive. In this superconducting state, the three t2g orbitals have very different superconducting form factors in momentum space. In particular, the intra-orbital pairing of the dx2-y2 orbital has an s-wave like pairing form factor. The two methods also predict very different pairing strength on different parts of Fermi surfaces. These results suggest that BaCoSO and related materials can be a new ground to test and establish fundamental principles for unconventional high temperature superconductivity.
